Documenting an inflation projection means writing down three inputs, the compound-inflation formula, and two outputs in one place so anyone (including future you) can retrace the calculation. The Inflation Calculator projects how a constant annual inflation rate changes the value of money over time, and every step of that projection is auditable because there are only three fields to capture. Future cost equals amount multiplied by (1 + r) raised to the power n, where r is the annual rate as a decimal and n is the number of years. Future purchasing power is the inverse: amount divided by (1 + r) raised to n, measured in today's dollars. Both formulas, both numbers, and the assumed rate all go in your notes. Because the model assumes a single constant rate for the entire period, the rate itself is the most important line to record, since change it and the entire result changes with it. Treating the calculator like a workpaper, capturing the input, showing the formula, writing the result, turns a quick estimate into a paper trail you can defend in a meeting or hand to a client.
What "Documenting the Steps" Actually Means for an Inflation Projection
Most "how do I document" questions for financial tools are really about creating a paper trail: enough information that someone else (an advisor, a co-author, a future version of yourself) can rebuild the same number from scratch. With an inflation projection, that paper trail is unusually short. There are three input fields, one formula, and two outputs. The Inflation Calculator returns both outputs in the same view, so the documentation challenge is not gathering numbers, but choosing which numbers to write down and in what order so the assumption chain is visible at a glance.
A good inflation audit note answers four questions without reopening the tool:
- What amount was used as the starting point, and in what currency?
- What annual rate was assumed, including the sign (positive for inflation, negative for deflation)?
- How many years forward was the projection run?
- Which of the two outputs is being cited, future cost or future purchasing power, and in what unit (nominal future dollars vs. today's dollars)?
If those four questions are answered in your note, the calculation can be reproduced. If any of them is missing, the result is a number without a context, and the next reader has to guess.
The Three Inputs and Two Outputs to Capture
The tool accepts exactly three inputs. Today's amount in dollars is the basket or balance you want to track forward in time. The annual inflation rate is the assumed constant percentage change per year, entered as a percent because the calculator applies the division to a decimal internally. The number of years is the projection horizon that becomes the exponent n. According to the product contract, amount and years must be zero or positive, while the rate may be negative to model deflation.
Two outputs are produced from those three inputs, and they are inverses of each other:
- Future cost answers "what will something priced at my amount today cost in n years?" It equals amount multiplied by (1 + r) raised to n.
- Future purchasing power answers the reverse: "what will my amount of cash actually buy in n years, measured back in today's money?" It equals amount divided by (1 + r) raised to n.
Documenting both is non-negotiable, because they are quoted in different units. Future cost is in nominal future dollars. Future purchasing power is in today's dollars. Confusing the two is the single most common documentation error in inflation work, and the easiest way to make the error is to record only one of them.
How to Document Inflation Calculator Steps in Order
This is the canonical sequence for an inflation projection note, in the order a reviewer will expect.
- Open the Inflation Calculator in a fresh browser tab and clear any old values from a previous run.
- Enter the starting amount in the dollars field. Write down the exact figure, including the currency, at the top of your note.
- Enter the assumed annual inflation rate as a percent (for example, 3 for 3%). Note the sign: a positive number is inflation, a negative number is deflation.
- Enter the number of years for the projection horizon. This becomes the exponent in both formulas.
- Read the future cost displayed in the result panel. Record it next to the label "Future cost (nominal, year n)" with the date the rate was assumed.
- Read the future purchasing power in the result panel. Record it next to the label "Future purchasing power (today's dollars)" so the unit confusion cannot happen.
- Date-stamp the note and, if the projection is part of a larger plan, link the rate source (CPI release, central bank statement, internal assumption) to the bottom of the entry.
Each of these seven lines belongs in the note. If you are documenting a projection for a client, the date stamp and the rate source are the two lines that turn a calculation into an audit-ready record. For a personal savings check, the date stamp alone is usually enough, but the same seven-line structure still applies.
| Line in the note | What to record | Why it matters |
|---|---|---|
| Date the rate was assumed | Day the calculator was run | Anchors the rate in time |
| Starting amount | Currency and exact figure | Both formulas start here |
| Annual inflation rate | Percent, sign included | Sign decides inflation vs. deflation |
| Projection horizon | Number of years | Drives the exponent in both formulas |
| Future cost | Nominal future dollars in year n | Answers "what will this cost later?" |
| Future purchasing power | Today's dollars in year n | Answers "what will this buy later, in today's money?" |
| Rate source | Internal note, CPI release, central bank statement | Audits the assumption itself |
Writing Down the Formula Behind the Result
A projection note that only lists inputs and outputs is incomplete. Anyone reading it later should be able to see the formula the tool applied, because that is the only way to confirm which version of "inflation" the projection used. The Inflation Calculator uses the standard compound-inflation model: future cost equals amount multiplied by (1 + r) raised to n, and future purchasing power equals amount divided by (1 + r) raised to n, where r is the annual rate in percent divided by 100 and n is the number of years.
A single worked example is enough to anchor the note. Take $100 today, 3% annual inflation, and 10 years. Future cost is 100 multiplied by (1.03) to the 10th power. (1.03) to the 10th is 1.3439, and 100 multiplied by 1.3439 is $134.39, meaning a basket of goods that costs $100 today will cost about $134.39 in 10 years. Future purchasing power is 100 divided by (1.03) to the 10th, or 100 divided by 1.3439, or $74.41, meaning $100 in cash will buy about $74.41 worth of today's goods in 10 years. Both figures appear in the calculator the moment you type the inputs, and writing them next to the formulas in your note is the moment a number becomes a record.
The 1.3439 factor that appears in both calculations is the compound-inflation multiplier for 3% over 10 years. Recomputing it in your note is what makes the document self-verifying: a reviewer can rebuild the multiplier, multiply by the amount, and arrive at the same $134.39 you wrote down. If the rebuilt number disagrees with the recorded number, the rate or the exponent in the note is wrong, and the error is caught before the projection is used in a decision.
Building a Multi-Scenario Audit Trail
The most common reason to document an inflation projection is to compare more than one rate at once: what does 2% do, what does 4% do, and what does 6% do over the same horizon? Each scenario is its own note, and the documentation discipline is to keep the starting amount and the years constant across scenarios so only the rate moves. That way, the difference between rows is provably the rate, not a hidden input change.
A clean layout is a single workpaper with the same amount and years in the header, and one row per rate scenario. For each row, record the rate, the (1 + r) to the n multiplier, the future cost, and the future purchasing power. The compound-inflation multiplier is the column that makes the table self-auditing, because the rest of the row is just amount multiplied by the multiplier and amount divided by the multiplier. Without the multiplier, a reviewer has to take the future cost on faith. With it, the row rebuilds itself on the back of an envelope. The exact figures for any rate and horizon come from the tool, so the multiplier column is best populated by running each scenario and writing the number down rather than by hand calculation.
If you are documenting the projection for someone else, include a short prose note above the table explaining which rate was chosen as the base case and why. A 20-year retirement check, for example, is often built around a 2% base case with 3% and 4% sensitivities. Writing the base-case rationale next to the table is what turns a sensitivity table into a decision record. For an even cleaner comparison workflow, the side-by-side charting approach in the Inflation Calculator chart guide keeps the same three inputs and reads out the same two outputs per row.
Deflation, Edge Cases, and the Limits Worth Flagging in Your Notes
Deflation is the easiest assumption to forget to document. The Inflation Calculator accepts a negative rate, so entering -2% gives a future cost below the starting amount and a future purchasing power above it, both of which look unusual on first read. The note must say, in plain language, that the rate is negative, what period the negative rate is meant to represent, and whether it is a one-off stress test or a sustained scenario. Without that line, a future reader of the note will assume the calculator malfunctioned.
Two other limits should be flagged in any inflation projection note. First, the model uses a single constant rate for the whole period, while actual inflation, measured by indexes like the Consumer Price Index, varies year to year according to the standard reference on inflation. A 3% projection is not a forecast of CPI; it is a what-if. Second, the calculator runs entirely in the browser, so no data leaves the device, but it also has no internal rate-of-rate model, no seasonality, and no separate column for a real-versus-nominal distinction beyond the two outputs. Those limits do not invalidate the projection; they just belong in the note so the reader does not over-read the result.
Finally, treat the output as general information, not as advice. Any inflation projection that feeds a real financial decision, a savings target, a salary ask, a retirement withdrawal rate, should be confirmed with a licensed professional. The documentation discipline that makes the calculator auditable is the same discipline that makes the advice that follows from it reviewable. For a deeper look at the traps to avoid while you are writing the note, the Inflation Calculator tips and common mistakes guide covers the most frequent input and unit errors in more detail.